Application Ser. No. 102,408, now U.S. Pat. No. 4,308,872, filed Dec. 11, 1979, entitled Method and Apparatus For Monitoring Respiration, the contents of which are incorporated herein by reference in their entirety, discloses a method and apparatus for quantitatively measuring respiration volume. The method disclosed in the application comprises looping first and second extensible conductors about the rib cage and abdomen, separately and simultaneously measuring the inductances of the conductors during respiration, weighting the measured inductances to reflect the differing contributions of the rib cage and abdomen to respiration volume, and summing the weighted measured inductances to obtain actual respiration volume.
As noted, practice of the technique disclosed in the application requires weighting or calibrating the inductances measured by the abdomen and rib cage conductors. To effect calibration it is necessary to determine the weighting factors K and L to satisfy the following equation: EQU V=K.multidot.RC+L.multidot.AB (Equation A)
where V is total respiration volume, RC is the rib cage contribution to respiration volume as measured at the rib cage conductor, and AB is the abdominal contribution as measured at the abdominal conductor. Application Ser. No. 102,408 discloses a specific technique for determining the values for the weighting factors K and L.
A spirometer is employed during the calibration procedure. With the patient in a first position, such as standing, a simultaneous set of readings are recorded from the outputs of the spirometer, the rib cage conductor, and the abdominal conductor. This is repeated with the patient in a second position, such as supine. At this point, there are two sets of values for V, RC, and AB which satisfy EQ. A. Thus, two equations having two unknowns, the constants K and L, may be written. From these, the weighting factors K and L may be determined by employing well known techniques for solving simultaneous equations. Thus: ##EQU1##
The denominators of EQS. B and C may, depending upon the recorded values, approach or equal zero. Clearly, when this happens, the values obtained for K and L will be inaccurate, thereby skewing any measurement based on such weighting factors. Thus, each time the denominators of equations B and C approach or equal zero, a new set of readings must be taken, thereby increasing the time required for calibration. It is therefore an object of the present invention to provide an improved calibration method and apparatus which avoids this drawback.